Without limiting the scope of the present invention, its background is described with reference to safety joints, as an example.
It is common practice in the wellbore drilling and completion arts to include a safety joint in a downhole tubular string to provide a point of separation in the tubular string such that the portion of the tubular string uphole of the safety joint can be retrieved to the surface while leaving the portion of the tubular string downhole of the safety joint in the wellbore. Safety joints are useful in a variety of circumstances. For example, safety joints are commonly used during the installation of certain tools, such as packers, in a wellbore. Similarly, safety joints are useful in allowing the recovery of a majority of the tubular string when an element of the tubular string below the safety joint become stuck or during fishing operations to recover a downhole element that was previously stuck in the wellbore, without the risk of sticking the entire recovery tubular string during the fishing operation.
Conventional safety joints have been operated using a variety of complicated or risky techniques. For example, certain safety joints have been operated by reciprocating the tubular string up and down while maintaining right-hand torque on the tubular string. In this design, the tubular string reciprocation and right-hand torque backs off a left-hand exterior threaded nut within the housing, which nut prevents the mandrel of the safety joint from coming free from the housing during normal tubular string movement. It has been found, however, that while this type of safety joint may be acceptable in some circumstances, there are occasions when the amount of right-hand torque which can be applied to a tubular string while reciprocating the string is limited by the ability of tools in the tubular string to withstand the required torque.
In another design, the safety joint is operated by neutralizing the weight of the tubular string at the location of the safety joint and rotating the tubular string to the right, which rotation backs off a left-hand exterior threaded nut within the housing. It has been found, however, that in certain wellbore configurations such as deep or deviated wellbores, torque does not transmit well along the tubular string such that the tubular string itself can be put under large amounts of force which can damage the tubular string.
In still other designs, the safety joint includes a release sleeve coupled to a mandrel with one or more shearable elements which must be parted by the application of a predetermined tensile or compressive force on the tubular string to enable the desired separation. It has been found, however, that the application of the required tensile or compression force on the tubular string elongates or compresses the tubular string prior to parting the shearable elements. Upon parting of the shearable elements, the tubular string violently recoils within the wellbore, which may cause damage to components in the wellbore or within the tubular string. In addition, it has been found, that during the recoil of the tubular string, the maximum allowable flowrate through certain components of the tubular string may be exceeded.
Accordingly, a need has arisen for an improved apparatus and method for disconnecting an upper part of a tubular string from a lower part of a tubular string during downhole operations. A need has also arisen for such an apparatus and method that enable separating the tubular string into two parts without the use of complicated or risky techniques. In addition, a need has arisen for such an apparatus and method that enable separating the tubular string into two parts without the need to perform rotations of the tubular string. Further, a need has arisen for such an apparatus and method that enable separating the tubular string into two parts without causing the tubular string to recoil due to tensile elongation.